enter code hereI am trying to install nettle library.
So, first I installed GMP library. Then I am trying to configure nettle libray and I am getting the warning below.

DNSSEC root key file in /etc/unbound/root.key was not found
This file is nedded for the verification of DNSSEC responses.
Use the command: unbound-anchor -a "/etc/unbound/root.key"
to generate or update it.

I tried to give

$apt-get update

But I always get 0% progress. it will not increase. (it is not connected to internet.)
Should I connected to internet? If so, it is not possible for me because my development system is always offline. Any download option is available from where I can download from other system and transfer to my development system?